1. Technical Field
The present invention relates to an electromagnetic coupling which transmits rotation from a drive shaft to a driven shaft.
2. Related Art
As a coupling (shaft coupler) for transmitting rotation from a drive shaft to a driven shaft, there is known an electromagnetic coupling which transmits the rotation from the drive shaft to the driven shaft by means of an electromagnetic action.
For example, JP 2008-245484 A discloses an electromagnetic coupling 100 as shown in FIG. 16. The electromagnetic coupling 100 comprises a first rotor 101 and a second rotor 102. The first rotor 101 has a circular column shape, and a permanent magnet is provided on an outer peripheral surface thereof. The second rotor 102 has an approximate circular cylindrical shape, and the first rotor 101 is inserted into a hollow portion of the second rotor 102. In the second rotor 102, a magnetic path 106 made of a material with a high magnetic permeability is provided on a structure 104 having a low magnetic permeability. As shown in FIG. 17, two (a pair of) magnetic paths 106 are provided in a circumferential direction of the second rotor 102, and three such pairs are provided along a rotational shaft direction of the second rotor 102.
The first rotor 101 and the second rotor 102 are housed in a housing 107. In a part of the housing 107 facing the second rotor 102, there is provided a core 110 around which a coil 108 is wound. When a current is applied to the coil, a magnetic flux is generated at the periphery of the coil 108. When the magnetic flux passes through the magnetic path 106 of the second rotor 102, the magnetic path 106 is magnetized.
When the first rotor 101 is rotated in this state, the permanent magnet provided on the first rotor 101 and the magnetized second rotor 102 are attracted to each other, causing the second rotor 102 to also rotate. In this manner, the rotation of the first rotor 101 is transmitted to the second rotor 102.
In addition, when an AC current is supplied to the coil 108, a rotational magnetic field is generated at the periphery of the coil 108. By applying the rotational magnetic field to the second rotor 102, it becomes possible to rotate the second rotor 102 at a rotation rate different from that of the first rotor 101. For example, when the rotational magnetic field is applied to the second rotor 102 along the rotational direction of the first rotor 101, the rotation rate of the second rotor 102 becomes greater than the rotation rate of the first rotor 101.
A reference, Toshie TAKEUCHI, “Analysis of EV/HEV Components, Vol. 10,” Nikkei Automotive Technology, Nikkei Business Publications, Jan. 1, 2011, No. 22, p. 102-105, discloses a motor which uses an electromagnet in place of a permanent magnet.
With regard to the rotor to which the rotational magnetic field is applied, if the ratio occupied by the magnetic path is small, there is a possibility that the magnetic coupling force with the other rotor becomes weak. An advantage of the present invention lies in provision of an electromagnetic coupling which can strengthen the magnetic coupling force between rotors as compared with the related art.